This invention relates to fuel injectors and more particularly to a fuel injector in which the pressures across the armature must be equalized.
During hot soak of liquid petroleum gas (LPG) and other high vapor pressure fuel vehicles having spark ignition, port injected engines, vapor leakage from the tips of the fuel injectors can fill the intake manifolds. This condition results in long starting times and can be attributed to a number of factors. For example, the manifold may fill with LPG vapors, little or no air may be present to support combustion, and the injectors may not be metering properly since they are calibrated to meter liquid; but may be filled with vapor.
Observations of injector rails and pods which were lifted out of intake manifolds during hot soak have shown that the injectors were being caused to open momentarily on a random basis during the hot soak period. This random nature of injector opening suggests that the filling of the intake manifold by vapor is not only due to simple leakage from the fuel injectors, but is largely caused by the fuel injectors opening when the engine is not running, and the injectors are under pressure. It seems likely that the displacement of this vapor is caused as a result of violent boiling of the high vapor pressure fuel in the fuel injector which creates a pressure differential across the armature, causing the armature to move, and thus open the valve. This phenomenon can occur because these high vapor pressure fuels can boil violently at relatively low temperatures.
Although vehicles which do not use these high vapor pressure fuels have been observed to have undesirable vapor formation in injectors as a result of engine heat, these vapors do not boil and "explode" as do the high vapor pressure fuels. Thus, the formed vapors are generally transported away from the injector by flushing them away in the return fuel through a fuel return path, as disclosed in U.S. Pat. No. 4,711,397 issued to Lahiff and U.S. Pat. No. 4,982,902 issued to Knapp et al. Although these vapor removal techniques are satisfactory for typical low vapor pressure fuels, such techniques do not address the problem of equalizing the pressure differentials created across an armature as a result of the violent boiling of high vapor pressure fuels.
It is therefore an object of the present invention to provide a fuel injector in which the differential pressure which typically occurs across the armature in vehicles using high pressure fuels can be avoided in order to reduce or eliminate the resulting liquid or vapor leakage from the fuel injector tip into the intake manifold.